1. Field of the Invention
The present invention relates to a centrifugal blower unit having a swirl chamber for converting the velocity energy of the air discharged from an impeller into pressure energy, and an electronic apparatus, such as a portable computer, equipped with the centrifugal blower unit.
2. Description of the Related Art
Portable electronic apparatuses such as portable computers are equipped with a microprocessor for processing various types of information. The amount of heat generated by the microprocessor is increasing more and more due to the increase in the processing speed and/or enhancement of versatility. Accordingly, to maintain the electronic apparatus in a stable state, it is necessary to increase the dissipation of heat from the microprocessors.
The apparatuses have a cooling unit for forcibly cooling the microprocessor. The cooling unit comprises a radiator section thermally connected to the microprocessor, and a centrifugal blower unit for applying cooling air to the radiator section, and is housed within a housing of the electronic apparatus.
The centrifugal blower unit comprises a rotary impeller and a casing that receives it. The casing has a suction port for allowing air to be drawn into the impeller, a swirl chamber containing the impeller, and a discharge port located at the downstream end of the swirl chamber.
When the impeller is rotating, the air inside the housing or external air is drawn into the impeller. This air is discharged from the outer periphery of the impeller into the swirl chamber by centrifugal force. In the swirl chamber, the air discharged from the impeller is guided to the discharge port, from which the air serving as cooling air is applied to the radiator section. The heat transmitted from the microprocessor to the radiator section is dissipated as a result of heat exchange using the cooling air, and is guided to the outside of the housing by the cooling airflow.
The swirl chamber of the casing serves to convert the velocity energy of the air, discharged from the impeller, into pressure energy. Thus, in the centrifugal blower units, the casing is extended radially outward with respect to the impeller, thereby gradually increasing the cross sectional area of the cooling air passage from the beginning to the end of the swirl chamber.
However, if the casing is extended radially outward with respect to the impeller, it inevitably has a large planar size. Therefore, the outer peripheral portion of the casing reaches a position above a printed wiring board mounted with the microprocessor, since the casing is housed in the housing adjacent to the printed wiring board. In general, a power supply circuit dedicated to the microprocessor is provided on the printed wiring board around the microprocessor. Tall circuit components such as coils, capacitors, etc. are disposed on the board, and thus interfere with the outer peripheral portion of the casing.